Method and apparatus for improving efficiency of high energy density batteries of metal-metal halide-halogen type by boundary layer

ABSTRACT

Efficiencies of high energy density batteries having metal and halogen electrodes and aqueous metal halide electrolyte are improved by creating a boundary layer of electrolyte low in halogen content adjacent to the metal electrode. Such boundary layer or stagnant electrolyte prevents contact of the metal electrode with halogen from a first flow of electrolyte containing dissolved halogen which passes through the base of the halogen electrode. When the cell is vertical, best formation of the boundary layer is obtained when the second flow of electrolyte enters the bottom of the cell and is directed upwardly and toward the halogen electrode with a horizontal velocity component equal to that of the first electrolyte flow entering the reaction zone. In preferred embodiments of the invention the cell comprises bipolar electrodes of zinc and a porous carbon base for the halogen, the halogen is chlorine and the electrolyte is aqueous zinc chloride.

United States Patent 1 [111 3,772,085 Bjorkman 5] Nov. 13, 1973 [54]METHOD AND APPARATUS FOR Primary Examiner-A. B. Curtis [75] Inventor:Harry K. Bjorkman, Birmingham,

Mich.

Occidental Energy Development Company, Madison Heights, Mich.

Filed: Nov. 18, 1971 Appl. No.: 199,911

Assignee:

Assistant Examiner-H. A. Feeley Attorney-William J. Schramm [57]ABSTRACT Efficiencies of high energy density batteries having metal andhalogen electrodes and aqueous metal halide electrolyte are improved bycreating a boundary layer of electrolyte low in halogen content adjacentto the metal electrode. Such boundary layer or stagnant electrolyteprevents contact of the metal electrode with halogen from a first flowof electrolyte containing dissolved halogen which passes through thebase of the halogen electrode. When the cell is vertical, best formationof the boundary layer is obtained when the second flow of electrolyteenters the bottom of the cell and is directed upwardly and toward thehalogen electrode with a horizontal velocity component equal to that ofthe first electrolyte flow entering the reaction zone.

In preferred embodiments of the invention the cell comprises bipolarelectrodes of zinc and a porous carbon base for the halogen, the halogenis chlorine and the electrolyte is aqueous zinc chloride.

10 Claims, 4 Drawing Figures 52 US. Cl 136/8 6 A [51] Int. Cl H0lm31/00, HOlm 29/02 [58] Field of Search 136/86 A, 86 S, 159, 136/160 [56]References Cited UNITED STATES PATENTS 2,921,110 l/1960 Crowley et al136/86 A 3,227,585 l/l966 Langford et al 136/86 E METHOD AND APPARATUSFOR IMPROVING EFFICIENCY OF HIGH ENERGY DENSITY BATTERIES OF METAL-METALHALIDE-HALOGEN TYPE BY BOUNDARY LAYER BACKGROUND OF THE INVENTION In theoperation of high energy density batteries of the secondary type,wherein halogen is caused to flow past an electrode base surface,creating a halogen electrode, it has been found that inefficiencies inthe production of electric current often result. Such inefficiencies andproductions of lesser currents by these batteries appear to beattributable to direct chemical reaction of the halogen with the metalon the surface of the other electrode of the cells. The reaction takesplace at the surface of the immobile material, the metal.

In diaphragm cells thin membranes of electrolytepervious material arepositioned between the anode and the cathode and the use of suchdiaphragms in the present cells can prevent most contacts of elementalhalogen with the metal electrode. However, physical difficulties ofconstruction, saggings and breakings of the diphragms with time, andtheir changes in permeability during use often make them impracticablefor the compact, thin, flat, bipolar electrode cells. Consequently,other mechanisms have been discovered and investigated in an effort toprevent undesirable contacts of halogen and metal, without the use ofphysical barriers between the electrodes.

SUMMARY OF THE INVENTION This invention relates to diaphragmlesssecondary cells for high energy density electric batteries in which thecontact of halogen with a metal electrode is prevented by utilization ofa stream or flow of electrolyte, which may be of lower halogen contentthan the main electrolyte flow and which is so directed into the cell asto counteract an appropriate velocity component of the main stream andprevent the electrolyte and halogen of that stream from impinging on theelectrode.

In accordance with the present invention, a diaphragmless secondary cellfor a high energy density electric battery comprises a cell frame, ametal electrode held to said frame, a supporting conductive electrodebase joined to the frame, means for contacting the supporting conductivebase with a halogen, aqueous metal halide electrolyte between theelectrode and the electrode base wherein the metal is that of the metalelectrode and the halide is that of halogen, means for moving theelectrolyte past the supporting electrode base and means for flowing anadditional quantity of electrolyte so as to produce a total electrolyteflow at a low Reynolds number adjacent to the metal electrode to createa boundary layer of electrolyte thereon which limits contact of thehalogen with the metal electrode. In preferred embodiments of theinvention a non-metal electrode base is of porous carbon, the metalelectrode is zinc on graphite and the aqueous electrolyte is zincchloride. Also, it is preferable that the second flow of electrolyteenter at the bottom of the vertical cell and be directed at an angle ofto 30 from the vertical so as to neutralize any horizontal flowcomponent of a first electrolyte flow into the cell reaction zone fromthe porous carbon electrode base.

DESCRIPTION OFTHE PREFERRED EMBODIMENTS The present invention and itsmode of operation will be readily apparent from the followingdescription, taken in conjunction with the accompanying drawing, inwhich:

FIG. 1 is a central vertical section of a diaphragmless secondary cellfor a high energy density electric battery, with the flows ofelectrolyte being indicated;

FIG. 2 is a side elevation of a bipolar electrode utilized, showing thepassageways through which electrolyte travels;

FIG. 3 is a flow vector diagram; and

FIG. 4 is a vertical sectional view, corresponding to that of FIG. 1,but illustrating a modification of the cell to provide for anelectrolyte of lower halogen content to be employed as that of thesecond electrolyte flow.

Electrolytic cell 11 includes two bipolar electrodes 13 and 15 heldtogether in a frame 17 and communicating through it with an electrolyteinlet duct 19 and an outlet manifold 21. Electrodes l3 and 15 each havea gas impervious and electrolyte-impervious wall 23 of graphite or otherconductive support or base material, which extends vertically, and onthe outer surface of which is layer or coating 25 of a metal, preferablyzinc. The inner surface of the wall is cemented or otherwise tightlyjoined to a perforated or porous base 27 for an electrode, preferably ofporous carbon. Together the impermeable supporting electrode part andthe perforated or porous part define a plurality of passageways 29running parallel to each other and vertically through the bipolarelectrode. Electrolyte 31, indicated in the reaction zone between themetal and porous or perforated carbon electrodes, passes into such zonefrom inlet duct 19, passageways 29 and through the base 27. Then, itpasses out exit 33 and out manifold duct 21, from which it may berecycled back to the electrode. In the preferred embodiment of theinvention wherein the metal electrode is zinc and the electrolyte isaqueous zinc chloride containing elemental or gaseous chlorine, it hasbeen noted that when the overall Reynolds number of the flow through thereaction zone 35 is low, indicating, non-turbulent flow, the dissolvedchlorine still reaches the zinc electrode 37 and chemically attacks it,causing a lowering of efficiency. Apparently, the transverse orhorizontal force, velocity or momentum given the electrolyte when itpasses into the reaction zone from the chlorine electrode base is strongenough that some of the electrolyte penetrates the normal boundary layeror film one would hope to have protecting the zinc. The disadvantage ofchemical attack on the zinc is also noted when the cell is beingcharged, during which period gaseous chlorine is produced at the porouscarbon electrode and is carried with electrolyte penetrating the layerabout the metal electrode. In fact, it has been considered that thechemical attack on the zinc may be more serious during charging but anysuch attack during discharge shortens the effective useful life of thebattery and therefore, from the consumers viewpoint, it is moredetrimental and should be avoided.

added to the reaction zone with a velocity or momentum componentopposite to the horizontal component of the first electrolyte velocityor momentum, preferably equal to it (and sometimes greater than it),good streamline flow is obtained, turbulence and eddy currents areminimized and the electrolyte moves upwardly through the cell withoutproducing detrimental boundary layer changes adjacent to the zincelectrode. Thus, there is produced a layer of stagnant electrolyte or aboundary layer against the zinc electrode and the chlorine, except forany that may be present in such layer initially, is prevented fromcontacting the zinc. It is desirable that the upward component of thevelocity of the second portion of electrolyte should be that desired togive proper flow through the reaction zone.

As illustrated in FIG. I, numeral 39 shows the direction of flow of thefirst electrolyte through the porous electrode into the reaction zoneand arrow 41 indicates the inclination upward of the flow of the secondportion of electrolyte. Arrows 43 indicate the resultant substantiallyvertical velocity. The second electrolyte portion flows through the sameinlet duct 19 as is used for the main portion and then passes through aninclined entrance duct 45 which gives it the desired heading upward andtoward the porous carbon electrode. It has been found that inclinationsfrom the vertical from 5 to 30 are most preferred for the production ofthe best stagnant lamina along the zinc electrode. Means for creatingthe desired flow is a pump, not illustrated, or other suitable mechanismfor circulating the electro lyte in the manner indicated.

It will be noted that at the top of the cell, passage 33 is located nearto the inner side of the porous carbon electrode. This is found to behighly desirable to also promote the flow of electrolyte along suchelectrode and away from the zinc electrode. After flow from the cell tothe manifold, the electrolyte may be recharged with chlorine andcirculated back to the inlet duct. During the charging cycle, chlorinemay be removed from the electrolyte and zinc chloride can be. added toit.

In FIG. 3 a vector diagram illustrates the neutralization of thehorizontal component of the velocity or momentum of the firstelectrolyte portion by an equal and opposite component of the upwardlydirected second electrolyte stream.

In FIG. 4 is shown a modification of the structure of FIG. 1 in whichall elements are the same except for means provided to circulate anelectrolyte containing less chlorine than that utilized in the processeffected with the structure of FIG. 1. Of course, for charging the cellit will be unnecessary to utilize the structure of FIG. 4 and, althoughit is not necessary that it be used for discharging, it may sometimes behighly desirable. Thus, in FIG. 4, it is seen that separate provisionsare made for entries of different types of electrolyte into the reactionzone. The first portion of electrolyte entering inlet duct 47 containsdissolved chlorine whereas that entering through duct 49 and passingthrough passageway 51, which second electrolyte will be closer to thezinc electrode, contains less dissolved chlorine or may even containnone of it. After the electrolyte is removed from the cell, throughpassage 53 and outlet manifold 55 it contains less dissolved chlorineand may be recycled back through duct 40 and passage 51, while anotherportion of this electrolyte may be recharged with chlorine and sent backto the cell through inlet duct 47 and the attendant passageways andpores through the porous carbon electrode. Of course, the structure ofthe apparatus of FIG. 4 is more complicated and often it will not beused, where the mechanism illustrated in FIG. I is sufficientlyeffective for the intended purpose.

In FIGS. I and 4 the means for contacting a nonmetal conductive basewith a halogen are passages or pores through the electrode base.Although the use of a porous electrode, preferably made from compressedand resin bonded activated carbon or graphite from which resin issubsequently removed, leaving the pores, is preferred, perforations mayalso be made in a more solid base, such as a graphite base. A graphitebase is preferably used for deposition of the zinc electrode thereon.The flow of electrolyte containing chlorine through the base and thecomparative dimensions of the reaction zone and inlet ducts andpassageways are such that the overall Reynolds number in the reactionzone is less than 1,000, although even higher Reynolds numbers areordinarily expected to yield non-turbulent flows. Strangely enough, ithas been found to be desirable to have even lower Reynolds numbers, lessthan 100, preferably 1 to 100 and most preferably, about I to 20.Generally, it is more important that the Reynolds number be low when thecell is being discharged than when it is being charged. In mostpreferred embodiments of the invention the velocity will be such thatthe Reynolds numbers will be less than 10 during discharge and less than20 during charging.

Instead of using a zinc electrode, other highly electropositive metalsmay be employed, such as nickel, chromium, iron, aluminum, copper, leadand magnesium. Instead of carbon and graphite electrode parts, stableand inert polymeric materials may be used, e.g., phenol formaldehyderesins, ABS resins, and natural and synthetic rubbers, e.g., chlorinatedrubber. The important thing is that such materials should withstand theelectrolyte and the halogen employed.

Instead of using zinc chloride and chlorine, zinc bromide and othermetal bromides and bromine may be used but the chlorine-zinc chloridesystems are highly preferred.

Various other materials which can be employed in making the structuresof the present invention and various advantages thereof and of thebipolar electrodes and cells of this general design are described inanother application for patent, filed the same day as the presentapplication, and entitled BIPOLAR ELECTRODE FOR CELL OF HIGH ENERGYDENSITY SECOND- ARY BATTERY, of which the present inventor is acoinventor. Such disclosure (Case U-l0-033 U.S. Ser. No. 200,041) is nowincorporated by reference in the present application. As in thatapplication, the porous carbon employed has a porosity such that acrosssection thereof comprises from 20 to percent carbon. The pores inor the passages through the porous carbon have an average diameter of 5to 300 microns and a least transverse thickness between the passagewaysand the reaction zone of from 0.3 to 3 millimeters. The distance betweenthe zinc electrode and the porous carbon base of the chlorine electrodeis from 0.3 to 3 mm. and the zinc is from 25 to 4,000 microns thick. Inthe reaction or generating zone the path pursued by the electrolyte issubstantially vertical, due to the inclination of the second portion ofthe electrolyte entering the zone. With the short distances between theelectrodes the importance of utilizing this means for separating thechlorine from the zinc is evident, since any appreciable velocity of theentering first electrolyte would be likely to cause the chlorine contentthereof to contact the zinc electrode.

Although, as illustrated, the electrodes are substantially vertical, asis the flow of electrolyte, in some embodiments it may be desirable toincline the cell from the vertical, even to have it substantiallyhorizontal. In such cases, the present invention is still applicable,with the directions of flow being modified accordingly, with allowancefor gravity effects.

The operation of the invention is considered to be evident from theforegoing description and the drawing. Those of skill in the artpracticing the invention will learn from experience how to adjust theproportions of flows through the different passageways and how to setthe angle of inclination of the second stream of electrolyte. Such anglemay be set by employing rotatable nozzles or deflectors in the variouschannels, which may be adjusted in position. Also, in some cases it maybe desirable to change the position of the entrance, preferably bymoving it nearer to the zinc electrode. In other cases, a secondentrance may be desirable to promote circulation at the non-metalelectrode and cause better contact of chlorine with such electrode. Thatis, the stream may be directed at such an electrode to increaseturbulence and prevent a stagnant boundary layer from forming thereon.However, this will usually not be necessary because of the sufficientturbulence caused by the electrolyte entering the reaction zone throughthe pores or perforations of the electrode. The second electrolytestream is usually a minor proportion of the electrolyte flow andtherefore, is usually at a higher compensating velocity, so that thehorizontal component counteracts the first electrolyte velocity. Ofcourse, inlet 51 for the second stream may be a single inlet or may beseries of smaller inlets located along the length of the zinc electrode.

The zinc chloride will be a saturated or nearly unsaturated solutioncontaining from 0.05 to 4 volumes of chlorine and will be at atemperature of 0 to 80C., preferably from to 40C. Sometimes, instead ofchlorine itself being present in the electrolyte, chlorine hydrate orother storage compound for chlorine may be present instead, preferablyin a decomposing state.

The principal advantage of the present structure, in addition toincreasing efficiency of charge and discharge of the cell and a batterymade from it and similar cells, is that its effect is obtained withoutthe use of diaphragms or other structures liable to deterioration orchange in properties during use. The simple flows, structures andmethods described are effective and the cells do not require tearingdown periodically for replacement of worn out parts. Also, there is aminimum of cell volume lost to effective generation of electricity,since the boundary layer is very thin, usually being from 0.01 to 0.1mm.

The following examples illustrate the operation of the present inventionbut do not limit it. It is clear that the structures and methodsdisclosed may be applied to other cells and batteries, such as thoseusing various metals, halogens and oxygen as electrode materials. Also,the metal electrodes may be replaced, rather than recharged with metal,so the second electrolyte flow may be set for best discharge operationonly. Unless otherwise indicated, all parts are by weight and alltemperatures are in C.

EXAMPLE 1 Following the teachings of U.S. patent application Ser. No.50,054, now U.S. Pat. No. 3,713,888, for HALOGEN I-IYDRATES and anapplication for patent filed the same day as the present application,identified as Case No. U 10,033 U.S. Ser. No. 200,041 for BIPO- LARELECTRODE FOR CELL OF HIGH ENERGY DENSITY SECONDARY BATTERY, in both ofwhich applications the present inventor is a co-inventor, adiaphragmless secondary cell for a high energy density battery isconstructed and is associated with other such cells to form a cell bankor battery. The construction of the cell is shown in FIG. 1 and is thesame as the cell of the co-filed application except for the provision inthe present case of a means for flowing electrolyte along the cathode toprevent the attack of chlorine on the zinc thereof. Thus, the electrodesare bipolar and comprise a negative electrode or cathode of zinc ongraphite, with the zinc being about 200 microns thick and the graphitebeing about 0.5 millimeter thick. The porous carbon has pores in the 25to 50 microns range, is of a porosity of about 45 to 50 percent and isabout five times as thick as the graphite. The channels cut or moldedinto the porous carbon are about half the thickness thereof.

The electrolyte is aqueous zinc chloride which has a zinc chlorideconcentration of from 15 to 35 percent, usually being 15 percent at thebeginning of discharge and the end of charge, and 35 percent afterdischarging and before charging. The electrodes have surface areas ofabout 170 square centimeters and are vertically positioned for bestoperations. The distance between the zinc electrode and the porouscarbon base of the chlorine electrode is about 2 mm. in these flat cellsand the flow rates of electrolyte through the porous carbon anode areabout 600 milliliters per cell per minute on charge and 400 mls per cellper minute on discharge. The electrolyte temperature is about 30C. andit contains about volume per cent of chlorine (one volume of chlorineper volume of electrolyte). The materials of construction utilized arephenol formaldehyde for the base parts of the cell and anelectrolyte-resistant cement for fastening the various parts together,which cement is preferably of the epoxy resin ester type (not aminecured).

The described cell is connected electrically in series with 23 othersuch cells so as to be capable of generating about 50 volts open circuit(40 volts at 8 amperes). The system is also connected so thatelectrolyte may be fed through the inlet manifold to each of the cellsand out the outlet manifold. The electrode design of FIG. 2 is employed.

The cells of the battery are charged by passing a 15 percent zincchloride aqueous solution through it at a flow of about 600 millilitersper cell per minute with application of the appropriate voltage, e.g.,50 volts, across the battery. Chlorine is generated at the anode andzinc is deposited on the graphite of the cathode. Such charging iscontinued for two hours, at which time the zinc has built up to about200 microns thickness in a smooth deposit without appearance ofdendrites or open areas on the electrode. In the absence of utilizingthe boundary layer control passageway of this invention, as when suchpassageways are blocked, it is sometimes found that objectionabledendritic formations appear on the zinc of the cathode and, duringdischarge, bare areas are noted and uneven dissolving of the zincresults, causing a less efficient operation.

The inclination of the boundary layer control passageway is exaggeratedin the drawing and is preferably at about 8 from the vertical, or justenough to counteract the horizontal momentum of the electrolytepenetrating the porous cathode. Relative volumes through the cathodesand the axillary port vary but usually less than 10 percent of theelectrolyte flow through the passageway designated as 51 will besufficient, in the present case such proportion being about 5 percent.In some runs this is increased for the purpose of getting bettercirculation at the cathode but such operations have the disadvantage ofalso increasing turbulence in the cell, thereby carrying some chlorineback into contact with the zinc, which causes pitting, localizedreactions and loss of power.

The boundary layer produced at the zinc surface by the describedelectrolyte flows is thin, usually being less than 0.1 mm., in theillustrated case being about 0.05 mm. The Reynolds number of flowadjacent the electrode is low, about 5 and almost always less than 100.During a similar discharging operation, the flow of electrolytedecreases approximately 50 percent.

The results of charging and discharging high energy density batterycells by the present invention are superior to results obtainablewithout the laminar flow of electrolyte in contact with the zincelectrode to place a non-stagnant but essentially slow moving film onit, protecting it from contact with chlorine passing through the porouselectrode on discharge or generated at it on charge. The zinc electrodesare more even and are more capable of producing high amperage at thedesignated voltage than are those wherein dendrites or voids arepresent. Additionally, by the method of this invention only one sourceof flow is required, because the electrolyte forming the film protectingthe zinc electrode comes from the same manifold as the activeelectrolyte cells.

EXAMPLE 2 The procedure of Example 1 is followed exactly, except for theutilization of the cell design of FIG. 4 in the high energy densitybatteries. As illustrated in FIG. 4, the electrolyte enteringpassageways Si is lower in chlorine content than the cell electrolytepassing through the porous carbon electrode. Thus, the slightdisadvantage of chemical reactions between the zinc of the electrode andchlorine in the electrolyte of the boundary layer is avoided. However, aseparate tank and circulation system for the chlorine-free electrolyteis required and in some cases, additional pumping facilities may bedesirable, although, as illustrated in the drawing, it is possible toutilize the pumping of the main body of electrolyte to create a suctionwhich carries the supplementary electrolyte into the cell to form itsprotective boundary layer adjacent the zinc cathode.

When operating with the same flow rates mentioned in connection withExample 1, it is considered that the deposition of zinc during dischargeis better than by following the procedure of Example 1 and similarly,the solubilizing of the zinc on discharge is more even.

The invention has been described with respect to illustrations andexamples thereof but it is clear that it is not to be limited to thesebecause equivalents may be substituted for elements or steps in theinvention without departing from the spirit of the invention or goingbeyond its scope.

What is claimed is:

l. A diaphragmless secondary cell comprising a cell frame having aninlet means and an outlet means, a metal electrode held to said frame, aporous supporting conductive halogen electrode joined to the frame andspaced from the metal electrode, thereby forming an intercell spacing,said cell frame outlet means being positioned between the metalelectrode and said halogen electrode of the cell, means for passing anaqueous metal halide electrolyte containing halogen into the cell frameinlet means, contacting the halogen electrode by passing the electrolytethrough the porous halogen electrode, into the intercell spacing and outthe cell frame outlet means, a second cell frame inlet means positionedadjacent to the metal electrode and spaced between the metal electrodeand the halogen electrode in the intercell spacing and inclined at anangle of 5 to 30 from the metal electrode and means for passingelectrolyte through the second inlet means towards the halogen electrodeso as to produce a total electrolyte flow at a low Reynolds numberadjacent to the metal electrode and to create a boundary layer ofelectrolyte thereon which limits contact of the halogen with the metalof the electrode.

2. A cell according to claim 1, wherein the frame is of a syntheticorganic plastic, the metal electrode is zinc, the halogen electrode isporous carbon, the means for contacting the halogen electrode withhalogen includes passageways for the halogen through the halogenelectrode and the aqueous metal halide is zinc chloride.

3. A cell according to claim 1, wherein the metal of the metal electrodeis affixed to the front of a carbonaceous substrate; the back of thecarbonaceous substrate is attached to the back of a second halogenelectrode of a second cell while the back of the halogen electrode isattached to the back of a second carbonaceous substrate for the metalelectrode of a third cell; the passageways for electrolyte are betweenthe back of each of the halogen electrodes and the back of each of thecarbonaceous substrates of the respective metal electrodes; theelectrodes are bipolar; the path pursued by the electrolyte through thefirst cell inlet means is through the passageways and through the poroushalogen electrode while the flow of electrolyte through the second cellinlet means is directed upwardly and towards the porous halogenelectrode so as to produce a vertical flow vector.

4. A plurality of cells according to claim 1, electrically connected toform a battery, with manifolds connecting electrolyte inlets and outletsof the cells.

5. A method of maintaining a boundary layer of an electrolyte adjacentto a metal electrode in a diaphragmless secondary cell having a cellframe having an inlet and outlet means, a metal electrode held to saidframe, a porous supporting conductive halogen electrode joined to theframe and spaced from the metal electrode, thereby forming an intercellspacing, said cell frame outlet means positioned between the metalelectrode and the halogen electrode of the cell, a second cell frameinlet means positioned adjacent to the metal electrode and spacedbetween the metal electrode and the halogen electrode in the intercellspacing and inclined at an angle of 5 to 30 from the metal electrodewhich comprises the steps of: (l) passing a halogen containing aqueousmetal halide electrolyte into said cell through the first cell frameinlet means, through the porous halogen electrode; (2) flowingelectrolyte into said cell through the second cell inlet means with sucha velocity as to counteract the flow of said halogen containingelectrolyte from said first inlet means in the direction of the metalelectrode, thereby insulating the metal electrode from the dissolvedhalogen containing electrolyte and (3) forcing both portions of theelectrolyte through the cell and out of the cell frame outlet means.

6. The method according to claim 5, wherein the cell is substantiallyvertical, the metal electrode is zinc on the front of a carbonaceoussubstrate, the back of the substrate being attached to the back of asecond porous halogen electrode of a second cell, while the back of thehalogen electrode is attached to the back of a second carbonaceoussubstrate of a second metal electrode of a third cell, the halogen ischlorine, the electrolyte is aqueous zinc chloride containing dissolvedchlorine, the electrodes are bipolar, passageways are formed between theback of the carbonaceous substrate of the metal electrodes and theporous carbon chlorine electrodes, wherein the electrolyte through saidfirst inlet means enters the cell with a substantially horizontalvelocity after passing through the chlorine electrode and theelectrolyte through said second inlet means enters the cell with upwardand horizontal velocity components so as to substantially neutralize thehorizontal velocity component of the electrolyte through said firstinlet means and move the electrolyte vertically past the zinc electrodeat a Reynolds number less than 100, and thereby insulate the metalelectrode from the chlorine of the electrolyte from said first inletmeans and maintain a boundary layer adjacent to the zinc electrode.

7. The method of claim 6, wherein the electrolyte flowing into the firstand second cell inlet means is from a common manifold means.

8. A method according to claim 6 wherein the electrolyte flow passingthrough said first inlet is substantially horizontal in the direction ofthe zinc electrode, the electrolyte flow passing through said secondinlet is at 5 to 30 from the vertical, and the velocity of theelectrolyte through said second inlet is greater than that of theelectrolyte from said first inlet.

9. A method according to claim 8, wherein the electrolyte passingthrough said second inlet enters the reaction zone of the cell at thebottom thereof adjacent to the zinc electrode.

10. A method according to claim 9, wherein the electrolyte passingthrough said second inlet is of a lower elemental chlorine content thanthe electrolyte passing through said first inlet.

2. A cell according to claim 1, wherein the frame is of a syntheticorganic plastic, the metal electrode is zinc, the halogen electrode isporous carbon, the means for contacting the halogen electrode withhalogen includes passageways for the halogen through the halogenelectrode and the aqueous metal halide is zinc chloride.
 3. A cellaccording to claim 1, wherein the metal of the metal electrode isaffixed to the front of a carbonaceous substrate; the back of thecarbonaceous substrate is attached to the back of a second halogenelectrode of a second cell while the back of the halogen electrode isattached to the back of a second carbonaceous substrate for the metalelectrode of a third cell; the passageways for elecTrolyte are betweenthe back of each of the halogen electrodes and the back of each of thecarbonaceous substrates of the respective metal electrodes; theelectrodes are bipolar; the path pursued by the electrolyte through thefirst cell inlet means is through the passageways and through the poroushalogen electrode while the flow of electrolyte through the second cellinlet means is directed upwardly and towards the porous halogenelectrode so as to produce a vertical flow vector.
 4. A plurality ofcells according to claim 1, electrically connected to form a battery,with manifolds connecting electrolyte inlets and outlets of the cells.5. A method of maintaining a boundary layer of an electrolyte adjacentto a metal electrode in a diaphragmless secondary cell having a cellframe having an inlet and outlet means, a metal electrode held to saidframe, a porous supporting conductive halogen electrode joined to theframe and spaced from the metal electrode, thereby forming an intercellspacing, said cell frame outlet means positioned between the metalelectrode and the halogen electrode of the cell, a second cell frameinlet means positioned adjacent to the metal electrode and spacedbetween the metal electrode and the halogen electrode in the intercellspacing and inclined at an angle of 5* to 30* from the metal electrodewhich comprises the steps of: (1) passing a halogen containing aqueousmetal halide electrolyte into said cell through the first cell frameinlet means, through the porous halogen electrode; (2) flowingelectrolyte into said cell through the second cell inlet means with sucha velocity as to counteract the flow of said halogen containingelectrolyte from said first inlet means in the direction of the metalelectrode, thereby insulating the metal electrode from the dissolvedhalogen containing electrolyte and (3) forcing both portions of theelectrolyte through the cell and out of the cell frame outlet means. 6.The method according to claim 5, wherein the cell is substantiallyvertical, the metal electrode is zinc on the front of a carbonaceoussubstrate, the back of the substrate being attached to the back of asecond porous halogen electrode of a second cell, while the back of thehalogen electrode is attached to the back of a second carbonaceoussubstrate of a second metal electrode of a third cell, the halogen ischlorine, the electrolyte is aqueous zinc chloride containing dissolvedchlorine, the electrodes are bipolar, passageways are formed between theback of the carbonaceous substrate of the metal electrodes and theporous carbon chlorine electrodes, wherein the electrolyte through saidfirst inlet means enters the cell with a substantially horizontalvelocity after passing through the chlorine electrode and theelectrolyte through said second inlet means enters the cell with upwardand horizontal velocity components so as to substantially neutralize thehorizontal velocity component of the electrolyte through said firstinlet means and move the electrolyte vertically past the zinc electrodeat a Reynolds number less than 100, and thereby insulate the metalelectrode from the chlorine of the electrolyte from said first inletmeans and maintain a boundary layer adjacent to the zinc electrode. 7.The method of claim 6, wherein the electrolyte flowing into the firstand second cell inlet means is from a common manifold means.
 8. A methodaccording to claim 6 wherein the electrolyte flow passing through saidfirst inlet is substantially horizontal in the direction of the zincelectrode, the electrolyte flow passing through said second inlet is at5* to 30* from the vertical, and the velocity of the electrolyte throughsaid second inlet is greater than that of the electrolyte from saidfirst inlet.
 9. A method according to claim 8, wherein the electrolytepassing through said second inlet enters the reaction zone of the cellat the bottom thereof adjacent to thE zinc electrode.
 10. A methodaccording to claim 9, wherein the electrolyte passing through saidsecond inlet is of a lower elemental chlorine content than theelectrolyte passing through said first inlet.